Method of treating mill-scale.



UNITED s 'rnrns PATENT our-ionrnnnnmcx M. menu, or unease ram-s. newroan, gssronon 'ro nnncrno METALLURGICAL comrmx, 0!." MAG or WESTVIRGINIA.

Ana mus, new Yong, A, qoaronarron METHOD 0! TREATING MILL-SCALE.

No Drawing.

Niagara and State of New York, have in- I vented certain new and usefulImprovements in Methods of Treating Mill-Scale, of which the followingis a specification.

In my prior Patents Numbers 1,081,566 and 1,081,570, patented December16, 1913, I have described certain processes applicable to the treatmentof ores, concentrates, or like products, of the iron-tungstate type, to

. obtain therefrom tungsten or its alloys in which the ratio of tungstento phosphorus,

expressed as g is materially higher than in the unreduced material.

The present invention relates to the application of processes of thiskind to the oxidized material known as high-speed millscale. This scaleis produced in considerable quantities as a by-product in themanufacture of high-speed steel, and consists, essentially, of oxidcompounds of iron and tungsten, usually with smaller proportions ofchromium and vanadium and containing also considerable quantities ofcobalt when derived from the so-called cobalt steels. The metals arepresent in the scale in the form of oxid, but are not, in all cases atleast, in their highest state of oxidation.

The following is the composition ot a typical high-speed mill-scale Iron57.66 per cent' Tungsten 12.25 Chromium 3.23 Vanadium 0.43 Manganese0.47 Silicon, 0.75 Carbon 0.35

Phorphorus 0.015 to 0.030

By smelting this scale with silicon as a reducing agent, in an electricfurnace and in accordance .with the methods disclosed in my priorpatents, it may be reduced to an alloy having approximately thecomposition of the steel from which the scale was originally derived.For example, partial analyses of a mill-scale and the alloy obtainedthere- Spaciflcatto'n 01' Letters intent.

Amman m d, 4 x;; 8.1914. Serial a. $30.41;.

Patented Feb. 2, 1915.

from by known processes of silicon reduction, are as follows MilLacale.Reduced alloy. Tungsten 11.90 15.60 Qhromium 2.90 3.40 Vanadium 0.49,0.43

The alloy so, obtained is utilizable as such, or, with appropriateadditions, it is available for themanufacture of steels of modifiedcomposition. I have found, however, that such high-speed mill-scalesusually contain a proportion of phosphoruswhich is distinctlyobjectionable. Moreover, the product of direct reduction of the scale iscomparatively low in tungsten: this of course necessitates the use of arelatively large proportion of the allo in compounding a given steel,fromv whic it results that the phosphorus-content of the steel is notmuch less than that of the alloy. These dificulties are avoided bytreating a millscale, before reduction, with an acid reagent whichserves the double purpose of removing iron, and thereb concentrating thetungsten-content, an of removing phosphorus, and thereby increasing theratio I have to nd that these mill-scales yield a large proportion oftheir iron, together with substantially all of their phosphorus, toacids, such as sulfuric acid, even in the cold. In other words, the veryhigh temperature to which they have been subjected in the course oftheir production has not resulted, as might be expected, in convertingthe iron into such an insoluble condition as occurs when iron-tungstateores are ignited or calcined. The process involving such acidtreatmentof the mill-scale is claimed in my copending application Serial No.830,417, filed concurrently herewith.

According to the present modification of the invention, the mill-scaleis subjected to a reducing operation before removing the phosphorus andconcentrating its tungstencontents. An illustrative example inaccordance with the present invention is as follows :The scale is groundto pass an eight-mesh screen and is mixed with about the theoreticalproportion of charcoal or other carbonaceous reducing-agent, calculatedupon its contents of wads of iron and tungsten. Theproportion ofcharcoal used should be so restricted as to avoid substantialcontamination of the reduced roduct by carbon, while efi'ecting as neary complete reduction of the iron and tungsten 'as may be practicablewithout such contaminainto a bath of sulfuric acid of 1.2 to 1.4specific gravity and digested for some hours, preferably with agitation.Following this digestion, the residue is'washed to remove the solublesulfate, dried, and smelted with a small proportion of silicon intheelectric furnace. Silicon is added in approximately the theoreticalproportions required for the reduction of such oxids as may haveremained unreduced as a result of the first treatment, avoiding suchexcess of silicon as would yield a reduced product undesirably high insilicon. Lime or other flux may be added in proportion to form with .thesilica a suitable slag, as is well understood in this art.

According to this method, up to ninety per cent. of thetotaliron-content may be extracted without entailing material losses oftungsten. The resulting alloys may contain up to sixty-five per cent. oftungsten or more according to the amount of iron removed-and are, forpractical purposes, free from phosphorus.

I claim:--

1. The herein-described method of preparing tungsten or its alloys fromhighspeed mill-scale containing tungsten, whichconsists in subjectingthe scale to a reducing-operation at a temperature below themelting-point of the reduced product, ex-

tracting a portion of the iron and thereby concentrating the tungsten insuch reduced product, and fusing the concentrate in an electric furnace.

2. The herein-described method of preparing tungsten or its alloys fromhighspeed mill-scale containing tungstem-which consists in subjectingthe scale to a reducing-operation at a temperature below the product andremoving phosphorus therefrom, and fusing the concentrate in anelectric'furnace in presence of a non-carbon reducing-agent.

Y 4. The herein-described method of preparing tungsten or its alloysfrom highspeed mill-scale containing tungsten, which consists insubjecting the scale to a reducing-operation at a temperature below themelting-point of the reduced product, concentrating the tungsten in suchreduced product and removing phosphorus therefrom by an acid reagent,and fusing the concentrate in an electric furnace in presence of anon-carbon reducing-agent.

5. The herein-described method of preparing tungsten or its alloys fromhighspeed mill-scale containing tungsten, which consists in subjectingthe scale to a reducing-operation at a temperature below themelting-point of the reduced product, concentrating the tungsten in suchreduced product and removing phosphorus therefrom by an acid reagent,and fusing the resulting purified concentrate in an electric furnace inpresence of silicon.

6. The method of preparing low-phosphorus tungsten or ferrotungsten fromhigh-speed mill-scale, which consists in partially reducing saidmill-scale, treating the reduced product to increase the ratio oftungsten to phosphorus, and thereafter completing the reduction.

In testimony whereof I aflix my signature in presence of two witnesses.

FREDERICK M. BECKET.

Witnesses:

J. A. HOLLADAY, G. C. FURNESS.

